Fertilizers that improve the
physical properties of the soil and, through these, influence the chemical and biological properties are amending. A
material that balances an anomalous texture or that gives structure to an inconsistent terrain or that improves its structural state stabilizing it is therefore to be considered a soil
conditioner. For example, the following materials are to
be considered as amendments to the specific context:
The amendments to the amendments for the modification of the weaving require substantial amounts of material, of the order of hundreds of tons per hectare for each decimeter of depth.
Even in the case of availability of low-cost material, the economic burden for transport, distribution and embedding is such that these interventions are not convenient and, in any case,
sustainable only on small surfaces and for special purposes. A secondary amalgamation effect occurs with reclamation
to fill when waters containing suspended material are used.
The amending interventions aimed at improving and stabilizing the structure require lower organic fertilizer inputs, of the order of tens of tons per hectare in case of extraordinary interventions or of a few tons per hectare in case of periodic interventions. The limited availability of organic soil improvers and the non-negligible costs of transport and distribution mean that these interventions are mostly carried out in specific contexts. In ordinary agricultural practice, by tradition, the supply of manure for soil improvers is carried out in the following cases:
They are corrective those fertilizers that improve the acidity of
the soil by shifting the pH from abnormal values towards neutrality. Potentially they have corrective action all those materials that are
constitutionally or physiologically acidic or alkaline. Lime
and limestone in acid reaction soils, and sulfur and gypsum in basic soils with constitutional alkalinity (calcareous soils) are traditionally considered corrective. The effectiveness of the corrections is conditioned by various factors:
The opportunity for corrective action is determined by real needs, economic sustainability and the intrinsic effectiveness of the intervention, especially in relation to the buffer power of the land. The competition of these factors makes it vary considerably according to the context:
For the above reasons, the opportunity of corrective interventions is evaluated almost exclusively for the correction of acid soils, also due to the more accessible cost of lime.
quantities necessary for the intervention can be estimated by means of chemical analysis, with the determination of the requirement at the bottom.
This determination, conducted in the laboratory, follows a standard procedure that differs more or less markedly from the actual operating conditions and, generally, the result in the laboratory
underestimates the actual needs, mainly due to the complexity of the factors involved in determining the power soil buffer.
In general, the cost of correcting an acid medium is such that it does not allow significant variations in the reaction, however, the increase of a few tenths of a pH unit may allow an expansion of the range of cultivable species to the point of making it economically convenient. correction.
Fertilizers that improve the endowment of the land in one or more elements of
fertility are fertilizers.
These fertilizers are therefore made in order to increase the endowment of a poor soil (bottom fertilization) or to meet the nutritional needs of a crop without incurring the depletion of soil
fertility (ordinary fertilization of production).
Fertilizers are the fertilizers most used in agriculture and their use is necessary above all in intensive agriculture, aimed at achieving high unit yields. In other conditions, the non-use of fertilization entails a slow but progressive impoverishment of the soil, which in more or less long periods undergo phenomena of intolerance. This problem is particularly felt in the tropical areas of the developing countries, where the cultivation of natural soils, in the absence of fertilization interventions, intensifies the process of desertification due to the modest absorbing power of the soil and the leaching of the nutritive elements in rainy climates.
The fertilizers are classified mainly according to the origin of the material and the chemical composition, with reference to the content in one or more main elements of fertility (nitrogen, phosphorus, potassium).
According to the first criterion, fertilizers are divided into three categories:
According to the second criterion, applied
fundamentally to chemical fertilizers, fertilizers are classified as follows:
The quantities of fertilizer used with the fertilizer are significantly lower than those made for an ameliorating effect or for a correction of the pH, this fact which often makes this
fertilization intervention profitable.
Fertilizer doses vary depending on various factors, such as the nature and title of the fertilizer, the needs of the crops, the expected quantitative and qualitative yields, the environmental
impact, the regulatory aspects, etc.
In the case of chemical fertilizers, the contributions are decidedly minimal, of a few quintals per hectare per year: excessively high doses have more or less serious negative effects on the production due to the increase in soil salinity, to any phytotoxicity, the onset of antagonistic phenomena between nutritive elements, interference with trophic relations between agrarian plant and parasites, etc. To these must be added any damage to the environment, mainly due to pollution of groundwater and potential health risks, related to the accumulation of nitrates in agricultural products.
In the case of organic fertilizers, provided with a much lower titer than chemical fertilizers, technically permissible doses are significantly higher and vary from a few tens of quintals per hectare per year to a few hundred. The factors limiting the quantities, in this case, are of an economic nature (excessive cost of transport and distribution), technical (low carbon-nitrogen ratio with consequent tendency to a rapid mineralization), environmental (risk of air pollution for the emanation of unpleasant odors and groundwater).
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